Voltage regulators, such as DC-to-DC voltage converters, are used to provide stable voltage sources for various electronic systems. Efficient DC-to-DC converters are particularly needed for battery management in low power devices (e.g., laptop notebooks, cellular phones, etc.). A switching voltage regulator generates an output voltage by converting an input DC voltage into a high frequency voltage, and then filtering the high frequency input voltage to generate the output DC voltage. Specifically, the switching regulator includes a switch for alternately coupling and decoupling an input DC voltage source (e.g., a battery) to a load (e.g., an integrated circuit (IC)). An output filter, typically including an inductor and a capacitor, may be coupled between the input voltage source and the load to filter the output of the switch, and thus provide the output DC voltage. A controller (e.g., a pulse width modulator, a pulse frequency modulator, etc.) can control the switch to maintain a substantially constant output DC voltage.
Lateral double-diffused metal oxide semiconductor (LDMOS) transistors are commonly used in switching regulators due to their performance in terms of a tradeoff between their specific on-resistance (Rdson) and drain-to-source breakdown voltage (BVd—s). For example, LDMOS transistors may be fabricated using processes, such as a Bipolar-CMOS-DMOS (BCD) process. In one LDMOS transistor approach, two different gate oxide regions can be formed under the transistor gate. One such oxide can be a conventional thin gate oxide, while the other oxide can be a thicker high voltage (HV) gate oxide. However, drawbacks of such an approach may include: (i) a relatively sharp step transitional region between the thin gate oxide and the thick HV oxide, which may be a reliability concern; and/or (ii) negative consequences on field isolation regions resulting from thinning of the field oxide (FOX) when the HV gate oxide is etched back during processing.